Bank cards, credit cards and other forms of electronic data cards have become more sophisticated over the years. In particular, it is now becoming more common to find display technology incorporated into such cards as well as other forms of smart cards, smart labels, and a variety of other devices. In this manner, such card devices may include a user-friendly display that may be employed in conjunction with the card. For example, the display may allow the card user to take advantage of security features such as one-time password (OTP) generation.
Unlike a laptop computer, personal digital assistant (PDA), or even a cell phone, electronic data cards, such as a conventional bank card, are generally lower cost items. That is, they may be mass produced and stored in bulk as “blanks”, devoid of any substantial electronic data prior to activation. In the case of a bank card, customer account access information may be loaded onto the card at the time of activation, for example, by the bank teller or the customer. Barring activation, however, the card remains a small, otherwise disposable, shelved blank of minimal value, with perhaps little care afforded to its manner of storage.
In light of the nature of electronic data cards as noted above, larger, more sophisticated, higher cost, and less durable display technology options may be avoided in providing display capacity thereto. For example, higher cost liquid crystal display (LCD), organic light-emitting diode (OLED), electroluminescence (EL), field emission display (FED), and other display technologies may be avoided. Rather, as noted below, the generally more durable, lower cost option of electrochromic display technology is often preferred.
An electrochromic display is one in which an electrochemical reaction takes place through an electro-active ink material such that pixels are activated to display a pattern in the form of letters, numbers, or other symbols. The display itself is of a stacked configuration that includes a transparent conductive frontplane positioned over a backplane. The backplane serves as a substrate to accommodate copper based circuitry for creating the image of the display whereas the electro-active ink material is provided thereon, sandwiched between the backplane and the transparent conductive frontplane.
As a cost reduction measure, fabrication of an electrochromic display preferably employs printing where possible. For example, a copper based backplane may be patterned and processed to form desired circuitry. This circuitry may provide electrical conductivity, form the pixels, and provide a means to attach a microprocessor and other electronic components such as resistors. Subsequently, a dielectric insulator may be printed over the circuitry to electrically isolate circuit traces within the backplane. Additionally, printing may be employed to provide silver circuit lines, carbon resistors, adhesives and other features on the backplane. The electro-active ink material may even be provided over the backplane by way of printing.
While printing does tend to reduce processing steps and increase throughput, other aspects of fabricating the electrochromic display tend to decrease efficiency. For example, as noted above, the circuitry employed in the backplane is generally traditional copper based flexible circuitry. While copper is an excellent conductor, it may be less than ideally suited to for the formation of pixels of an electrochromic display. That is, in addition to certain topography issues, copper is susceptible to erosion by the electro-active materials and presents a challenge to forming electrical connections such as to a microprocessor via wirebonding. Thus, additional processing is often employed to cover the underlying copper circuitry. For example, processing may include additional steps to plate a gold barrier over the copper in order to avoid ultimate breakdown of the display circuitry and to allow wirebonding of the microprocessor.
Unfortunately, however, techniques for providing gold or other non-copper metals onto traditional copper based substrate add process steps to the fabrication of the display. This reduces throughput and similarly increases fabrication costs. Furthermore, the addition of copperless metals may lead to thicknesses exceeding 20-25 microns thereby presenting a significant challenge to achieving a standard resolution of about 4 mil circuit lines.